package network;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 86131
 * Date: 2024-04-23
 * Time: 9:59
 */
public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动!");
        while (true) {
            //1. 读取请求并解析
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096],4096);
            socket.receive(requestPacket);  //从此套接字接收数据报填写到requestPacket（如果没有接收到数据报，该方法会阻塞等待
            //为了方便在Java代码中处理,可以把上述数据报中的二进制数据拿出来构造成String
            String request = new String(requestPacket.getData(),0, requestPacket.getLength());

            //2. 根据请求计算响应
            String response = this.process(request);

            //3. 把响应写回到客户端
            DatagramPacket responsePacket = new DatagramPacket(response.getBytes(),0,response.getBytes().length,
                                   requestPacket.getSocketAddress());
            socket.send(responsePacket);

            System.out.printf("[%s:%d] req=%s, resp=%s\n",requestPacket.getAddress(),requestPacket.getPort(),request,response);

        }
    }

    //由于当前写的是"回显服务器",直接返回原来的数据
    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }

}
